Complementary push-pull amplifier device with protective circuit means

ABSTRACT

In an amplifier device including a driving amplifier circuit and a push-pull output circuit, the push-pull output circuit consisting of a first amplifier portion which turns &#34;on&#34; when the drive current of the driving amplifier circuit decreases, and a second amplifier portion which turns &#34;on&#34; when the drive current increases, the improvement comprising the first protective circuit which is disposed on the input side of the first amplifier portion so as to branch an input current when the first amplifier portion falls outside its allowable operating range, and the second protective circuit which is disposed on the input side of the driving amplifier circuit so as to branch an input current when the second amplifier portion falls outside its allowable operating range, whereby even when the drive current of the driving amplifier circuit becomes large, the constituent parts of the push-pull output circuit can be reliably protected from being destroyed.

This is a continuation of application Ser. No. 413,223, filed Nov. 6,1973 and now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to amplifier devices. More particularly,it relates to an amplifier device which includes at least a drivingamplifier circuit and a push-pull output circuit, the push-pull outputcircuit consisting of a first amplifier portion which turns "on" whenthe drive current of the driving amplifier circuit decreases, and asecond amplifier portion which turns "on" when the drive currentincreases.

2. Description of the Prior Art

In the field of the amplifier devices of this type, many power amplifierdevices recently developed have amplifier circuits which are directlycoupled and employ the OTL system in order to put them into the form ofintegrated circuits. With such a construction, however, a great currentflows through the push-pull output circuit. Therefore, a loadshort-circuit, for example, may result. Then, the power amplifierportions forming the push-pull output circuit fall outside the allowableoperating ranges, and their constituent components are thereforedestroyed.

In an example of a measure for solving such a problem, when the firstand second power amplifier portions fall out of the allowable operatingranges, changes in the voltage and current on their output side aredetected. The respective inputs of the first and second amplifierportions are adjusted on the basis of the detection, whereby theoperations of the amplifier portions are controlled. The circuit thusfar described is shown in a Japanese technical periodical"Denshi-Gijutsu (Electronics)," No. 2, Vol. 14, 1972, FIG. 6, in a paperentitled `Circuit Design viewed from Protecting System` on pp. 34 - 39.

With such a construction, the destruction of the transistors of thefirst and second amplifier portions due to overloads for the first andsecond amplifier portions, or due to an abnormal rise in the supplyvoltage, can be prevented. However, in the case of overloads, forexample, the drive current at the output of the driving amplifiercircuit becomes large. It is accordingly feared that the transistorconstituting the driving amplifier circuit will fall into an overloadedstate, leading to its destruction.

In order to solve the problem, a circuit has been proposed in which theinput of the driving amplifier circuit is adjusted at the overloadcondition. With any of such constructions, however, protective circuitsare so arranged as to separately control the input sides of therespective constituent parts. As a consequence, the required number ofcomponents is large, and the structure is complicated.

Besides, in the prior-art constructions, the transistors of theprotective circuits disposed on the input sides of the first and secondamplifier portions differ in type. For example, when a P-N-P transistoris used on the input side of the first amplifier portion, an N-P-Ntransistor is employed on the input side of the second amplifierportion. Accordingly, in the case where the power amplifier device ofsuch construction is to be produced in the form of an integratedcircuit, it is required to make either of them in the lateral structureand the other in the vertical structure. This is undesirable from thepoint of view of raising the degree of integration.

SUMMARY OF THE INVENTION

It is therefore the principal object of the present invention to providean amplifier device of simple construction in which, even when the drivecurrent of the driving amplifier circuit for driving a push-pull outputcircuit becomes large, the output transistors of the push-pull outputcircuit can be reliably protected.

Another object of the present invention is to provide an amplifierdevice which has a protecting function suitable for integrating apush-pull output circuit.

Still another object of the present invention is to provide an amplifierdevice which can reliably protect the transistors of a push-pull outputcircuit with a small current.

Yet another object of the present invention is to provide an amplifierdevice which can use a driving amplifier circuit having a high voltagegain.

In order to accomplish such objects, the present invention provides aprotective circuit on the input side of a driving amplifier circuit sothat, when the second amplifier portion falls out of the operatingrange, its output may be controlled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 4 are schematic circuit diagrams each showing an embodimentof the amplifier device according to the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a power amplifier device which is an embodiment of theamplifier device according to the present invention. In the figure, Q₁ -Q₁₁ designate transistors, among which the transistors Q₁, Q₂ and Q₈ areof the P-N-P type, and the other transistors are of the N-P-N type. R₁ -R₁₇ indicate resistances, C₁ - C₇ capacitors, D₁ - D₃ diodes, IN aninput terminal, V_(cc) a power source terminal, and SP a speaker.

The transistors Q₁ and Q₂ have their emitters connected in common. Thetransistors Q₃ and Q₄ are so connected as to constitute constant-currentloads of the transistors Q₁ and Q₂. These components form a differentialamplifier along with the resistance R₄, and perform a pre-amplificationfunction. The transistors Q₆ and Q₇ and transistors Q₈ and Q₉ are in theDarlington connection, respectively. The transistors Q₆ - Q₉ constitutea complementary push-pull output circuit. The base of the transistor Q₆is connected through the resistance R₉ and R₈ to the power sourceterminal V_(cc), while the base of the transistor Q₈ is directlyconnected to the collector of the transistor Q₅ performing a drivingamplification function. The emitter of the transistor Q₇ is connectedthrough the resistance R₁₀ to the collector of the transistor Q₉, whilethe emitter of the transistor Q₉ is grounded through resistance R₁₁. Asregards the transistor Q₅, the collector is connected to the base of thetransistor Q₆ through the diodes D₁ - D₃ for supplying an idlingcurrent, the emitter is grounded, and the base is connected to thecollector of the transistor Q₁ constituting a part of the aforesaiddifferential amplifier. Between the juncture P of the resistances R₈ andR₉ and the juncture Q of the resistance R₁₀ and the transistor Q₉, thereis connected a capacitor C₅, which constitutes a bootstrap circuit alongwith the resistances R₈ and R₉.

The transistors Q₁₀ and Q₁₁ are transistors which constitute ASOdetection type protective circuits, which are the characterizing featureof the present invention. The transistor Q₁₀ has its collector connectedto the base of the transistor Q₆, has its emitter connected to thejuncture Q, and has its base connected through the resistance R₁₄ to theemitter of the transistor Q₇. The base of the transistor Q₁₀ isconnected to the juncture of the resistance R₁₂ and R₁₃ being connectedin series between the power source terminal V_(cc) and the juncture Q,and thus receives a predetermined bias. The transistor Q₁₁ has itscollector connected to the base of the transistor Q₅, has its emittergrounded, and has its base connected through the resistance R₁₇ to theemitter of the transistor Q₉. The base of the transistor Q₁₁ isconnected to the juncture of the resistances R₁₅ and R₁₆ being connectedin series between the juncture Q and ground, and thus receives apredetermined bias. The capacitor C₇ interposed between the collectorand base of the transistor Q₅ is for phase compensation. The resistancesR₆ and R₇ and the capacitor C₇ constitute a negative feedback circuit.

In this circuit configuration, transistor Q₅, resistances R₈ and R₉,diodes D₁ -D₃, and capacitors C₅ and C₇ constitute a driving amplifiercircuit DA; transistors Q₆ and Q₇ constitute a first amplifier portionAP₁ ; and transistors Q₈ and Q₉ constitute a second amplifier portionAP₂. Resistances R₁₀, R₁₂, R₁₃ and R₁₄ constitute a first detectingcircuit DT₁ ; resistances R₁₁, R₁₅, R₁₆ and R₁₇ constitute a seconddetecting circuit DT₂ ; transistor Q₁₀ constitutes a first protectivecircuit means PR₁ ; and transistor Q₁₁ constitutes a second protectivecircuit means PR₂. The base of the transistor Q₅ acts as an input of thedriving amplifier circuit DA, a juncture of the resistance R₉ and diodeD₁ acts as a first output of the driving amplifier circuit DA, and thecollector Q₅ acts as a second output of the driving amplifier circuitDA. The bases of the transistors Q₆ and Q₈ act as inputs of the firstand second amplifier portions AP₁ and AP₂, respectively. The firstdetecting circuit DT₁ is connected in series with the first amplifierportion AP₁ between a first d.c. voltage source Vcc and an outputjuncture Q of the push-pull output circuit. The second detecting circuitDT₂ is connected in series with the second amplifier portion AP₂ betweenthe output juncture Q of the push-pull output circuit and a second d.c.voltage source GND.

The first and second detecting circuits DT₁ and DT₂ detect the outputcurrent and the voltage drop of the first and second amplifier portionsAP₁ and AP₂, and generate first and second detected signals at thejunctures of resistances R₁₂ and R₁₃, and R₁₅ and R₁₆, respectively.

The first protective circuit means PR₁ is connected to the input of thefirst amplifier portion AP₁, and the second protective circuit means PR₂is connected to the input of the driving amplifier circuit DA.

When, for example, the speaker SP, serving as the load of this device,is short-circuited under such a construction, the transistors Q₁₀ andQ₁₁ having the protecting function operate as described below.

When the input of the transistor Q₅ decreases and the collector current(drive current) I_(d) of this transistor decreases, the base potentialof the transistor Q₆ rises. Accordingly, the transistor Q₆ and thetransistor Q₇ become more saturated. The emitter output current of thetransistor Q₇ increases, so that the base potential of the transistorQ₁₀ rises. Thus, the base current of the transistor Q₆ can be controlledwith the collector current of the transistor Q₁₀.

When the input of the transistor Q₅ increases and the drive currentI_(d) of this transistor increases, the base potential of the transistorQ₈ lowers. Accordingly, the transistor Q₈ and the transistor Q₉ reach amore saturated state, to increase the emitter output current of thetransistor Q₉. Therefore, the base potential of the transistor Q₁₁rises. Consequently, the transistor Q₁₁ starts conducting, and the basecurrent of the transistor Q₅ can be controlled with the collectorcurrent of the transistor Q₁₁. In this case, the transistor Q₁₁ needadjust only as small a current as 1/h_(FE) (h_(FE) : the currentamplification factor of the transistor Q₅) of the drive current I_(d).The collector potential of the transistor Q₅ can be sufficientlycontrolled, and the protecting operation can be reliably effected.Accordingly, such a construction makes it unnecessary to separatelyincorporate protective circuits onto the input sides of the respectiveconstituent parts as in the prior art.

With such a construction, the transistors Q₁₀ and Q₁₁ may be of the sametype. Moreover, they are of the N-P-N type. It is therefore unnecessaryto employ the transistor of the lateral structure as in the prior art.Since the transistors of the vertical structure can be used as theprotective circuits, the current amplification factor can be madecomparatively large. Accordingly, control signals which serve as inputsto the protective circuits may be small.

That is, even in the case where, in order to enhance the voltage gain ofthe amplifier device, the emitter resistance of the transistor Q₅ ismade small (it need not be incorporated) and the drive current is madevery large for the current drive, the protecting operation can besecurely performed.

FIG. 2 shows another embodiment of the amplifier device according to thepresent invention. A point of difference from the embodiment in FIG. 1is that the push-pull output circuit is of the pure complementary type.In the figure, Q₁₂ and Q₁₃ indicate P-N-P transistors, which are in thepure complementary connection with the transistors Q₆ and Q₇. D₄designates a diode.

With such a construction, the transistors Q₁₀ and Q₁₁ perform theprotecting operation similar to that in the embodiment in FIG. 1.

FIG. 3 shows a power amplifier device which is another embodiment of theamplifier device according to the present invention. In the figure,Q₃₁ - Q₄₁ represent transistors, among which the transistors Q₃₅, Q₃₈,Q₄₀ and Q₄₁ are of the P-N-P type and the transistors Q₃₁ - Q₃₄, Q₃₆,Q₃₇ and Q₃₉ are of the N-P-N type. R₃₁ - R₅₂ designate resistances,C₃₁ - C₃₇ capacitors, and D₃₁ - D₃₅ diodes.

The transistors Q₃₁ and Q₃₂ have their emitters connected in common. Thetransistors Q₃₃ has its collector connected to the commonly connectedemitters, and has its emitter grounded through the resistance R₃₄. Thecollector of the transistor Q₃₁ is connected through the resistance R₃₅to a power source terminal V_(cc), while the collector of the transistorQ₃₂ is directly connected to the power source terminal V_(cc). Theresistances R₃₁ - R₃₃ serve to determine the base bias of the transistorQ₃₁. The resistance R₃₈ and the diodes D₃₄, D₃₅ are connected in seriesbetween the power source terminal V_(cc) and ground, and drive as aconstant-current source the transistor Q₃₃ whose base is connected tothe juncture between the resistance R₃₈ and the diode D₃₄. Thesecomponents constitute a differential amplifier, and perform apre-amplification function.

The transistors Q₃₆ and Q₃₇ and transistors Q₃₈ and Q₃₉ are connected soas to constitute a complementary push-pull circuit. The collector of thetransistor Q₃₇ is connected through the resistance R₄₀ to the powersource terminal V_(cc). The emitter of the transistor Q₃₈ and thecollector of the transistor Q₃₉ are connected through the resistancesR₅₁ and R₄₁ to the emitter of the transistor Q₃₇, respectively. Theemitter of the transistor Q₃₆ is connected through the resistance R₄₉ tothe emitter of the transistor Q₃₇, the collector of the transistor Q₃₈is grounded through the resistance R₅₀, and the emitter of thetransistor Q₃₉ is directly grounded.

The transistor Q₃₅ performs a driving amplification function for theforegoing push-pull output circuit. It has its emitter connected to thepower source terminal V_(cc), its collector connected to the collectorof the transistor Q₃₄ through the diodes D₃₁ - D₃₃ for supplying anidling current, and its base connected to the collector of thetransistor Q₃₁. The emitter of the transistor Q₃₄ is grounded throughthe resistance R₅₂, while the base is connected through the resistanceR₃₉ to the juncture between the resistance R₃₈ and the diode D₃₄.Accordingly, the transistor Q₃₄ is adapted to operate as aconstant-current source.

The transistors Q₄₀ and Q₄₁ form ASO detection type protective circuitswhich constitute the characterizing feature of the present invention. Asregards the transistor Q₄₀, its emitter is connected to the power sourceterminal V_(cc), its collector is connected to the base of thetransistor Q₃₅, and its base is connected through the resistance R₄₄ tothe collector of the transistor Q₃₇. As regards the transistor Q₄₁, itsemitter is connected to the emitter of the transistor Q₃₇, its collectoris connected to the base of the transistor Q₃₈, and its base isconnected through the resistance R₄₇ to the collector of the transistorQ₃₉. The base of the transistor Q₄₀ is connected to the juncture betweenthe resistances R₄₃ and R₄₂ being connected in series between the powersource terminal V_(cc) and the emitter of the transistor Q₃₇, while thebase of the transistor Q₄₁ is connected to the juncture between theresistance R₄₆ and R₄₅ being connected in series between the emitter ofthe transistor Q₃₇ and ground. Thus, the bases of the transistors Q₄₀and Q.sub. 41 receive predetermined biases. The capacitor C₃₇incorporated between the base and collector of the transistor Q₃₅ is forphase compensation. The resistances R₃₇ and R₃₆ and the capacitor C₃₄constitute a negative feedback circuit.

With such a construction, the transistors Q₃₆ and Q₃₇ are renderedconductive when the drive current of the transistor Q₃₅ becomes large.Therefore, the transistor Q₄₀ can branch the base current of thetransistor Q₃₅ in dependence on the variation of the drive current.Accordingly, the operation of the transistor Q₄₀, the operation of thetransistor Q₄₁ and the effect thereby attained are similar to those inthe case of FIG. 1, and therefore the detailed explanation is omitted.

FIG. 4 shows a power amplifier device which is a further embodiment ofthe amplifier device according to the present invention. Particularly,it illustrates a different ASO detection type for the protectivecircuitry.

In the figure, Q₅₁ - Q₆₆ designate transistors, among which transistorsQ₅₃, Q₅₄, Q₅₆ and Q₆₂ are of the P-N-P type and transistors Q₅₁, Q₅₂,Q₅₅, Q₅₇ - Q₆₁ and Q₆₃ - Q₆₆ are of the N-P-N type. R₆₁ - R₇₇ indicateresistances, C₅₁ - C₅₉ capacitors, and D₅₁ - D₅₇ diodes.

The transistors Q₅₁ and Q₅₂ are emitter-coupled. On the collector side,the transistors Q₅₃ and Q₅₄ are connected so as to constitute aconstant-current load. Connected to the coupled emitters is a seriescircuit consisting of the transistor Q₅₅ and the resistance R₆₄, theformer of which has the base bias determined by the diodes D₅₄ - D₅₇ andthe resistances R₆₁ and R₆₂. These components constitute a differentialamplifier, performing a pre-amplification function.

The transistor Q₅₆ performs a level shift function. It has its baseconnected to the collector of the transistor Q₅₂, has its emitterconnected to a power source terminal V_(cc), and has its collectorconnected to a series circuit consisting of the resistance R₆₅ and thetransistor Q₅₇ whose base bias is determined by the same means as in theforegoing transistor Q₅₅.

The transistors Q₆₀ and Q₆₁ and transistors Q₆₂, Q₆₃ and Q₆₄ constitutea push-pull output circuit. The transistors Q₅₈ and Q₅₉ are in theDarlington connection, and constitute a driving amplifier circuit.

The transistors Q₆₅ and Q₆₆ constitute protective circuits,respectively. The transistor Q₆₅ has its collector connected to the baseof the transistor Q₆₀, has its emitter connected to the juncture Rbetween the emitter of the transistor Q₆₁ and the collector of thetransistor Q₆₄, and has its base connected through the resistance R₇₂ tothe emitter of the transistor Q₆₀ and the base of the transistor Q₆₁. Inthis case, the base of the transistor Q₆₅ is connected to the junctureof the resistances R₇₆ and R₇₃ connected in series between the powersource terminal V_(cc) and the juncture R, and thus receives apredetermined base bias. On the other hand, the transistor Q₆₆ has itscollector connected to the base of the transistor Q₅₈ performing adriving amplification function, has its emitter grounded, and has itsbase connected through the resistance R₇₄ to the emitter of thetransistor Q₆₃ and the base of the transistor Q₆₄. The base of thetransistor Q₆₆ is connected to the juncture of the resistances R₇₇ andR₇₅ connected in series between the juncture R and ground, and thusreceives a predetermined base bias.

Also with such a construction, the transistors Q₆₂ - Q₆₄ are renderedconductive when the drive current of the transistors Q₅₈ and Q₅₉ becomelarge. Therefore, the transistor Q₆₆ can adjust the base current of thetransistor Q₅₈ in dependence on the variation of the drive current. Theother operations and the effect thereby accomplished are the same as inthe foregoing cases. In FIG. 4, the part enclosed by dotted lines isconstructed of an integrated circuit. Numerals enclosed with circlesindicate terminal numbers.

In this circuit configuration, transistors Q₅₈ and Q₅₉, and resistancesR₇₀ and R₇₁ constitute the driving amplifier circuit DA; transistors Q₆₀and Q₆₁ constitute the first amplifier portion AP₁ ; and transistorsQ₆₂, Q₆₃ and Q₆₄ constitute the second amplifier portion AP₂.Resistances R₇₂, R₇₃ and R₇₆ constitute the first detecting circuit DT₁; resistances R₇₄, R₇₅ and R₇₇ constitute the second detecting circuitDT₂ ; transistor Q₆₅ constitutes the first protective circuit means PR₁,and transistor Q₆₆ constitutes the second protective circuit means PR₂.

The base and the collector of the transistor Q₅₈ act as the input andthe output of the driving amplifier circuit DA, respectively.

Although, in the foregoing embodiments, the present invention is appliedto the push-pull output circuits of the Darlington complementary type,it may of course be applied to those of the mere complementary type.

Although, in the embodiments described herein, the driving amplifiercircuits are of the current drive type, they may of course be of thevoltage drive type.

Although, in the embodiments, the protective circuits are of the ASOdetection type, they may of course be of the current limit type. In thiscase, the first and second detecting circuits detect only the outputcurrent of the first and second amplifier portion. For example, in FIG.1, the first and second detecting circuits consist of resistance R₁₀ andR₁₁, respectively.

Although, in any of the embodiments, the present invention is applied toa power amplifier device, it may be applied to general amplifiercircuits, such as an operational amplifier device for industry.

As described above, in accordance with the amplifier device of thepresent invention, even when the drive current of the driving amplifiercircuit is large, the transistors of the push-pull output circuit can bereliably protected with a circuit of simple construction. Since all thetransistors for protecting the transistors of the push-pull outputcircuit can be made in the same type, the integration of the device isfacilitated. In accordance with the present invention, the transistorsof the push-pull output circuit can be reliably protected with smallcurrents, so that the integration of the device is facilitated. Inaccordance with the present invention, the voltage gain of the drivingamplifier circuit can be made high.

While I have shown and described several embodiments in accordance withthe present invention, it is understood that the same is not limitedthereto but is susceptible of numerous changes and modifications asknown to a person skilled in the art, and I therefore do not wish to belimited to the details shown and described herein but intend to coverall such changes and modifications as are obvious to one of ordinaryskill in the art.

What I claim is:
 1. In a complementary push-pull amplifier device withprotective circuit means including at least a driving amplifier circuitand a push-pull output circuit connected to the output of said drivingamplifier circuit, the push-pull output circuit consisting of a firstamplifier portion and a second amplifier portion, wherein inputs of saidfirst and second amplifier portions are respectively connected to theoutput of said driving amplifier circuit,so that said first amplifierportion is rendered conductive and said second amplifier portion isrendered non-conductive respectively when the drive current of saiddriving amplifier circuit decreases, and said first amplifier portion isrendered non-conductive and said second amplifier portion is renderedconductive when the drive current of said driving amplifier circuitincreases, the improvement comprising: a first detecting circuitconnected in series with said first amplifier portion between a firstd.c. voltage source and an output juncture of said push-pull outputcircuit; a second detecting circuit connected in series with said secondamplifier portion between said output juncture of said push-pull outputcircuit and a second d.c. voltage source; first protective circuitmeans, connected to the input of said first amplifier portion andresponsive to a first detected signal of said first detecting circuit,for controlling the input of said first amplifier portion, when saidfirst amplifier portion falls out of its allowable operating range; andsecond protective circuit means, connected to the input of said drivingamplifier circuit and responsive to a second detected signal of saidsecond detecting circuit, for controlling the input of said secondamplifier portion when said second amplifier portion falls out of itsallowable operating range.
 2. A complementary push-pull amplifier devicewith protective circuit means as defined in claim 1, wherein said firstand second amplifier portions each comprises a respective pair oftransistors in the Darlington connection.
 3. A complementary push-pullamplifier device with protective circuit means as defined in claim 1,wherein said first and second amplifier portions each comprise arespective pair of transistors of the complementary type.
 4. Acomplementary push-pull amplifier device with protective circuit meansas defined in claim 1, wherein said first protective circuit meanscomprises a first transistor connected between the input of said firstamplifier portion and said output juncture of said push-pull circuit,and said second protective circuit means comprises a second transistorconnected between the input of said driving amplifier circuit and saidsecond d.c. voltage source.
 5. A complementary push-pull amplifierdevice with protective circuit means as defined in claim 4, furtherincluding a differential amplifier circuit connected to the input ofsaid driving amplifier circuit.
 6. A complementary push-pull amplifierdevice with protective circuit means as defined in claim 4, wherein aconstant current source is connected to the output of said drivingamplifier circuit which is connected to the inputs of said first andsecond amplifier portions.
 7. A complementary push-pull amplifier devicewith protective circuit means as defined in claim 6, further including adifferential amplifier circuit connected to the input of said drivingamplifier circuit.
 8. A complementary push-pull amplifier device withprotective circuit means as defined in claim 4, wherein said drivingamplifier circuit comprises a pair of transistors connected inDarlington configuration.
 9. A complementary push-pull amplifier devicewith protective circuit means as defined in claim 8, wherein a levelshift circuit is connected to the input of said driving amplifiercircuit.
 10. A complementary push-pull amplifier device as defined inclaim 1, wherein each one of said driving amplifier circuit and saidfirst amplifier portion comprises at least one transistor of a firstconductivity type, and said second amplifier portion comprises at leastone transistor of a second conductivity type, opposite said firstconductivity type.
 11. A complementary push-pull amplifier device asdefined in claim 10, wherein each of said first and second protectivecircuit means comprises at least one transistor of said firstconductivity type.